This invention relates to an attachment for a telephone subscriber's terminal equipment and, in particular, to an attachment that completely suppresses the ring of the bell in the terminal equipment, which otherwise would occur in response to an incoming call, until the calling party is identified.
U.S. Pat. No. 3,936,617 issued to Bolgiano, discloses a system for selectively deactivating a telephone bell on a telephone instrument such that when a telephone number is called, an auxilliary system automatically cuts in to prevent ringing of the bell until a predetermined code is initiated, i.e. until the caller is identified, by the calling station. The telephone bell is actuated only when the caller is identified. The system includes a relay which operates to disconnect the phone instrument from the phone line, thereby theoretically preventing the bell in the instrument from operating (ringing). A flip-flop is used to open the bell ringer circuit causing a transistor to saturate so that the normally closed relay will open. However, due to inherent delays in switching when a ringing signal is first detected, the bell may actually ding when the normally closed relay opens. Furthermore, the open circuit produced by the opening of the relay does not satisfy the electrical current requirements for billing protection as explained in Section 68.314 (c) of the Federal Communications Commission (FCC) Rules and Regulations which are incorporated herein by reference. Section 68.314 (c) says that, for subscriber billing purposes, loop current through the subscriber's terminal equipment in the off-hook state, i.e. when answering an incoming call:
(1) must be at least as great as the current through a 200 ohm resistance connected across tip and ring conductors in place of the terminal equipment, or PA1 (2) must not decrease by more than 25 percent from its maximum value during at least a five (5) second interval immediately following the beginning of the off-hook state. Simply opening the relay in response to an incoming call does not satisfy the requirements of Section 68.314 (c) nor does it prevent the bell from dinging thereby alerting the subscriber to an incoming call before the calling party is identified.
Other relevant U.S. patents include U.S. Pat. Nos. 4,001,708 and 4,006,316 both issued to Bolgiano. Other references include the Bell System Communications Technical Reference, Pub. 47001, August 1976, and the FCC's, Part 68 Interconnection Standard 50-769-02, July 6, 1981.
Therefore, it is an object of this invention to completely suppress the dinging of the telephone bell when an incoming call is received and detected by a subscriber's terminal equipment until the calling party is identified.
An object of this invention is to completely suppress the dinging of the subscriber's telephone bell while at the same time permitting required loop current to flow through the subscriber's terminal equipment to provide for subscriber billing protection.
Normally, a telephone company central office applies negative battery to the ring conductor and ground to the tip conductor in a subscriber's terminal equipment. However, during the progress of an incoming call, the polarity of the calling station or called party line may be reversed depending on the type of call and type of switching system, i.e. step-by-step, in the central office.
Therefore, another object of the invention is to provide complete bell suppression regardless of whether the telephone company central office battery polarity is reversed.